Bolometer construction



April 14, 1953 A. A. OBERMAIER 2,634,609

BOLOMETER CONSTRUCTION Filed NOV. l2, 1947 Patented pr. 14, 1953 oLoMETER CONSTRUCTION Alfred A. Gbermaier, Chicago, Ill., assigner to Illinois Testing Laboratories, Inc., Chicago, Ill., a corporation of Illinois Application November 12, 1947, Serial No. 7 85,240

4 Claims.

vMy invention relates, generally, to the constru-ction of bolometers, and it has particular relation to ionization type bolometers and methods of operating the same.

Among the objects of my invention are: To vary the number of molecules of a gas available for ionization as a function of temperature; to measure the resultant current flow which is a function of the temperature; to contain the gas in an ionization chamber and to bombard its molecules with alpha particles emitted by radioactive material in the chamber; to increase the sensitivity of the device by employing a radiation receiver in the chamber; to employ a pair ofvspaced electrodes in the chamber between which a unidirectional electric eld is maintained forcausing current iow therebetween; and to measure such current flow by thermionic means.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

. My invention is disclosed in the embodiments thereof shown in the a-ccompanying drawing and it comprises the features of construction, combination of elements, arrangement of parts, and method of operation which will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scopeA of my invention reference can be had to the following detailed description, taken together with the accompanying drawing, in which:

.Figure 1 is a detailed sectional view taken along the line I-I of Figure 2 and illustrating somewhat diagrammatically a preferred form of bolometer construction;

. Figure 2 is a detail sectional view taken along the line 2--2 of Figure 1;

`Figure 3 illustrates, diagrammatically, the bolometer construction shown in Figures l and 2 Vand also how the current flow therethrough as a function of temperature can be measured by thermionic means;

AFigure 4 shows a curve which demonstrates the operating characteristics of the bolometer shown in the preceding figures; and

.Figure 5 illustrates, diagrammatically, an alternate bolometer construction and how it may be connected to a measuring circuit.

Referring now particularly to Figures 1 and 2 of the drawing, it will be observedthat the reference characcter I0 designates, generally, a bolometer of the ionization type constructed in accordance with my invention. The bolometer I0 includes an ionization chamber II that may be formed of quartz or it may be formed of metal with a window of quartz for receiving radiant energy. The ionization chamber lating liquid I2, such as carbon tetra-chloride. For a given temperature the space I3 above the surface of the liquid I2 contains a certain number of free molecules or vapor in equilibriumy with the surface of the liquid. As the temperature inside of the ionization chamber II in` the space I3 by .bombarding the same with alpha.

particles emitted from a foil of radioactive material chamber II. The number of ionized molecules of the gas in the space I3 also is a function of the temperature.

As shown in the drawing, an electrode or grid.

I5 and an electrode or plate I6 are positioned in insulated spaced relation within the ionization chamber II and, as will be described hereinafter, they are maintained at a predetermined relative unidirectional potential so that an electric eld is generated therebetween. .When the` potential of the plate I6 is higher than that of the grid I5, the ionized molecules are attracted to the former and thus a now of current takes place therebetween. The current flow is a function of the number of ionized molecules which, in turn, is a function of the temperature within the ionization chamber II.

The bolometer I0 is made more sensitive byl the provisionk within the chamber II of a radiation receiver I'I in the form of athin strip of' copper or gold covered with lamp black. The radiation receiver I'I readily absorbs the radiant energy falling thereon and effects a corresponding in-crease in temperature of the gas inA the:

I I is' evacuated and then filled with a volatile insu-v I 4 also located within the ionization.

With the bolometer vlll con-'- structed as described, the radiant energy thusreceived by the radiation receiver I'I increases I.

the number of molecules available for ionization in the space I3 in direct proportion to the amount of energy received. By measuring the current ow between the electrodes I5 and I6, it is possible to obtain an indication of the amount of radiant energy received. Accordingly, the electrodes I5 and I5 are connected to terminals I9 and Zit, respectively, between which there is maintained a difference of unidirectional potential su-ch as a potential of 150 volts.

When the electrodes I5 and I6 have the unidirectional potential applied theretovasillustratedin Figure 3, the current now therebetween is proportional to the temperature withinl the chamber II which in turn is proportional to the vapor density therein. The relationship between the vapor density within the ionization chamber II and the current i'lowing between the electrodes I5 and I6 is indicated by the curve 2l in Figure 4. Tests have shown that the slope of the curve 2Ii is constant regardless of ther ambient temperature.

In orderV to measure the current ow between the electrodes I5 and I5, the electrometer 22 of the thermionic type in Figure 3 may be used. The electrometer 22 includes a. pair of electric valves 23 each of which includes an anode 23a, a, control grid 23g, and a hot cathode 23e. cathodes 23C may be interconnected by a resistor 214i Whose midpoint is connected through a resistor 25 toi ground and to negative terminal I9. The electrode` I5 may be connected to one of the grids 23g, as shown, and through a resistor 25 to a point alongV a voltage dividing resistor El, connected betweenV the terminals Iii and 20, where a biasing voltage of about 65 volts is applied to the grids 23g.

The null method of measurement is employed and for this purpose a galvanometer 29 having a,

pointer 30 and a scale 31 may be employed. The galvanometer 29 is connected between anode resistors 32, as illustrated. At a given temperature the system is adjusted by a variable resistor 33 so that the pointer 30 is positioned at the zero point relative tothe scale 3 I Now as radiant energy is received byY the radiation receiver I1 in the bolometer Il), the number of molecules available for ionization by the radioactive material id is increased correspondingly and there is a corresponding increase in the current flow between the electrodesv I5 and I6. The pointer 35 moves up the scale 3|.' which may be calibrated in units of pressure orV temperature as desired.

Another embodiment of my invention is shown in` Figure 5. The bolometer I", there shown, is similar to the bolometer IIl except for the omissonof the electrode or grid I and the position-v ing; of the radiation receiver Il to one sideY of the ionization chamber II. rIhe plate or anode I6 is connected directly to one of the grids 23g of the electrometer 22 while the radioactive material Ill is ungrounded. When soV arranged and connected, the bolometer IB functions as a. Faraday cage. with the charge thereof being a function of the radiant energy applied to the receiver I1. This effects a corresponding control of the conductivity of the associated valve 23 which is reected in the indication provided by the galvanometer 29.k

Since certain further changes can be made in the foregoing constructions and methods and diierent embodiments of the invention can be made without departing from the, spirit and scope thereof, it is intended that all matter shown irrthey accompanyingdrawing. and describedV here- Y 'Thev inbefore shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. Apparatus of the class described comprising, in combination, an evacuated container having a wall through which radiant energy is adapted to be received into the container and containing a volatile rlioiuid from which free molecules of vapor are liberated bythe temperature within the container and in amount which changes according to changes in temperature. radioactive material within the container and operable to ionize, independently of the radiant energy, the free molecules of vapor liberated from the Volatile liquid, an electrical circuit having a source of electricl energy therefor and including therein an electrodel disposed within said container and having current ow developed therein in response to the ionized molecules of vapor` and in amount which is a function of the number of ionized molecules, and an electrical indicating instrument in circuit withl said electrode.- for in,- dicating by the amountv ofv current'` flow in said? circuit the amount of radiant energy received into,- said container.

2. Apparatus according to claim 1 wherein the,v electrodev is in the formv of a plate element. andi wherein thereis a grid element disposed-1 within the container in spaced relation to said' plate element and connected to said electrical circuit;

for generation of an electrical field between the grid element and said' plate-element;

3. Apparatusv of the class describedY comprising. in combination, an evacuated container contain-f ing a volatile liquid 'from which free molecules. ofvapor are liberatedby the temperature within. the container and in amount which changes-according to changes in temperature, said container having a wall through which radiant energy mayf enter the container, radioactive material within the container and operable to ionize, independently of the radiant energy, the free-molecules of vapor liberated from the volatile liquidi, an electric circuit including thereinl an electrode disposed within said container-and having-'a current flow developed therein in response tothe ionized molecules of'vapor, an electrical indicate ing instrument in said circuit, and a radiationy receiver disposed within the container andof' a character to absorb radiantV energy entering the container to eiect a corresponding increase intemperature therein, whereby't'oincrease the-'sen-l sitivity of the device.

4. Apparatus of the class described comprising; in combination, an evacuatedcontainer containing a volatile liquidy from which free molecules of vapor are liberated by the-temperature withinthe container and in amount which changes according to changes in temperature, said container having a Wall through which radiant energy may enter the container, radioactive-material within the container and operable to ionize,l independently of the radiant energy, the free molecules of vapor liberated from the volatile'- liquid, an electrical circuit including therein an` electrode disposed within-saidcontainer'and having current flow developedv therein inv response*A to the ionized molecules ofv vapor, an electrical indicating instrument in said circuit, saidl electrode being in the form of a plate-element, agrid element disposed within the container in' spaced relation to said plate element and connected to said electrical circuit for generation of an electrical fieldi between the grid element' and' said' plate element, and a radiation receiver disposedl 5 within the container and of a character to absorb radiant energy entering the container to eiect a corresponding increase in temperature therein, whereby to increase the sensitivity of the device.

ALFRED A. OBERMAIER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,372,798 Buckley Mar. 29, 1921 1,566,279 King Dec. 22, 1925 Number Number 

